Encapsulated supported coils



March 29, 1966 1.. E. LAWRENCE 3,243,752

ENCAPSULATED SUPPORTED COILS Filed March '7, 1962 5 Sheets-Sheet 1INVENTOR LELAND E. LAWRENCE sv/mrd/ ATTORNEY March 29, 1966 LAWRENCE3,243,752

ENGAPSULATED SUPPORTED COILS Filed March '7, 1962 5 Sheets-Sheet 2INVENTOR LELAND E. LAWRENCE ATTORNEY 5G F Z2 H M W W I March 29, 1966 E.LAWRENCE 3,243,752

ENCAPSULATED SUPPORTED (JOILS Filed March 7, 1962 5 Sheets-Sheet 5\NVENTOR LELAND E.LAWRENCE ATTORNEY March 29, 1966 E. LAWRENCE 3,243,752

ENCAP SULATED SUPPORTED GOILS Filed March 7, 1962 5 Sheets-Sheet 4INVENTOR LELAND E. LAWRENCE ATTORNEY March 29, 1966 L. E. LAWRENCE3,243,752

ENCAPSULATED SUPPORTED COILS Filed March '7, 1962 INVENTOR LELANDE.LAWRE'.NCE

ATTORNEY United States Patent 3,243,752 ENCAPSULATED SUPPORTED COILSLeland E. Lawrence, Wauwatosa, Wis., assignor to Allen- Bradley Company,Milwaukee, Wis., a corporation of Wisconsin Filed Mar. 7, 1962, Ser. No.178,094 3 Claims. (Cl. 336205) The present invention relates to themanufacture of electrical coil assemblies, and particularly to coils foruse in electromagnetically operated devices, wherein the manufacture ofsuch coils may comprise the steps of winding a predetermined number ofinsulated conductor turns on an insulating supporting tube, the turnsbeing in juxtaposed, layer wound relation; interleaving strips ofinsulat ing paper, or the like, between the wound layers; affixing theconductor leads to a terminal strip; mounting a coil or coils on alocating and supporting plate, which may be adapted for use as amagnetic shunt, with a removable die insert to protect screw threads;and molding an encapsulating, insulating coating around the coil orcoils and the supporting plate by means of transfer molding techniques,or the like, said coating being of such nature as to retain therespective turns and layers in close relative proximity withoutpenetrating internally of the coil winding layers.

In coils of previous constructions vacuum impregnation with varnish, ormore lately with an epoxy resin, has been used to hold the wire turnsfirmly in place to prevent vibration caused by alternating magneticfields or mechanical shock. This method effectively holds the wire turnsin place, but it has some disadvantages. Any coil so constructedcontains a substantial amount of resin in the interstices of the windingwhich upon accidental overheating gives off quantities of heavy smokewhich may condense on associated parts of the switch or other equipmentnearby. Also, such a 'coil may drip resinous products of decompositionon associated or nearby equipment. Further, and this is particularlytrue of coils impregnated and cast with epoxy resin as encapsulatingmaterial, such coils tend to swell, blister and deform, in addition toexuding resinous material, so that they are often very difficult toremove from their associated structure for purpose of replacement. Also,in coils of this construction,

the magnet wire in the coil which is generally insulated with some formof resinous coating, is subjected to the action of solvents in thevarnish or of liquid epoxy resin for considerable time duringimpregnation and curing at elevated temperatures. This may tend tosoften the insulation on the wire and reduce its effectiveness.

It is an object of this invention to produce a coil wherein the turnsare held securely against vibration by compacting the winding underhydrostatic pressure during a molding process in which an encapsulatingmaterial is caused to surround the windings under fluid pressure untilit cures to a solid mass.

It is another object of this invention to produce a coil which,containing no impregnating resin the intertices of the winding, andutilizing an encapsulating resin resistant to heat, gives off relativelysmall amounts of smoke, exudes little, if any, resinous material, anddoes not swell or blister objectionably when accidentally overheated.

Among other objects of the present invention is the provision of apressure-molded coil assembly which is completely protected againstmechanical damage and harmful atmospheres.

sults in a coil assembly for use in electromechanical devices, and whichassembly is encapsulated for protection against mechanical damage andthe damaging effects of "ice deleterious atmospheric conditions, andwherein the coil or coils will not swell objectionably if subjected toovervoltage conditions which result in overheating.

It is a further object of the present invention to provide anelectromagnetic coil assembly which is encapsulated with a moldingmaterial of high thermal conductivity capable of readily dissipatingheat, and which further provides an effective seal for a coil or coilscontained therein.

It is another object of the present invention to provide anelectromagnetic coil assembly which includes a coil or coils which havebeen layer wound to provide a compact and neatly assembled constructionadaptable for placement in molding dies wherein a pressure moldingcomposition may be used to entirely encapsulate the assembly and tomaintain the individual coil turns in juxtaposed relationship.

It is still another object of the present invention to provide aprotective outer layer for a coil assembly of a molding compositionapplied by means of transfer molding techniques or the like, whereinsaid composition is in contact only with the end turns, so as tominimize any deleterious effects on the previously applied coil wireinsulation.

It is another object of this invention to provide, as an integral partof a coil assembly, a mechanical support member which aids andfacilitates manufacture of the coil assembly, adds to the mechanicalstrength of the coil assembly, and which may be adapted to provide amagnetic shunt path for controlling the shape of the pull curve of themagnet of which the coil assembly is a part.

It is a still further object of the present invention to provide a coilassembly which has such precision of dimension that the coil itselfprovides structural usage, such as support of certain components in thecase of electrical motor starter or the like.

It is still another object of the present invention to provide a coilassembly which lends itself to clean, straightforward productiontechniques.

The fore-going and other objects and advantages of'this invention willappear from the description following, which is set forth by referenceto the accompanying drawings, in which there is set forth by way ofillustration and not of limitation, a procedure of manufacture and aform in which this invention may be embodied.

In the drawings:

FIGS. 1-13 inclusive, are illustrative of a sequence of manufacture ofan encapsulated coil assembly in accordance with teachings of thepresent invention, and wherein;

FIG. 1 is a perspective view of a preformed rectangular coil tube whichserves as a support for the coil turns,

FIG. 2 is a diagrammatic view of portions of a winding apparatus and, inparticular, illustrating the procedure for winding turns around the coiltube and interleaving of insulating paper strips between winding layers,

FIG. 3 is an end view of the coil tube relative to FIG. 2 with thesupporting tube in sliding fit engagement with an elongated windingmandrel, and further illustrating the relationship of the layer woundcoil turns and interleaving insulating paper strip,

step of seating cooperating coil members on a common support-plate,which'plate may be adapted for use as a magnetic shunt,

FIG. 7 is atop plan view of an assembly of twin coils seated on thesupport plate, and with the coils being connected in aiding seriesrelationship by means of twisting their adjacent leadstogether,

FIG. 8 is a perspective view of a terminal assembly to be fastened toone side of the coil construction by means of adhesive engagement withthe outermost insulating paper layer,

FIG. 9 is aperspective view of the coil assembly with the two remainingleads of the respective coils fastened to thethreaded terminal members,and further illustrating the step of mounting a protective moldinginsert in threading engagement with openings in the terminal assembly,

FIG. 10 is'a front elevational view of the coil assembly and itsprotective moldinginsert just prior to being placed "inits respectivecavity of a transfer molding machine,

FIG. 11 is a fragmentary view of a transfer molding machine illustrativeof the means for interim support of the coil assembly during the periodthat the encapsulating molding composition is entering the die cavities,

FIG. 12 is a view similar to FIG. 11 of the apparatus and illustratingthe step of withdrawing supporting molding pins after sufficient moldingcompound has been forced into the die to provide equal pressure upon allsurfaces of the coil assembly to be encapsulated thereby, I FIG. 13 is afragmentary view of the molding machine "illustrating the steps ofremoving the finished, encapsulated coil assembly from its respectivedie cavity after the molding composition has been brought to finalcuring state,

FIG. 14 is a perspective view of the finished encapsulated-coil assemblymade in accordance with the teachings ofthe present invention,

' FIG. 15 is an elevational view of the finished coil assembly having aportion broken away to more specifically illustrate the article in itsfinal form, and with the protective molding'insert removed from theterminal assembly,

FIGS. 16, 17 and 18 are views respectively taken along lines 1616, 1717and 1818 of FIG. 15, and in which various details of the coil portionsare more clearly disclosed.

As mentioned previously, the various steps in the pre- -'ferred methodof manufacturing the coil assembly of the present invention aredisclosed in FIGS. 1-13, in-

clusive. With reference to FIG. 1, the coil members of the present coilassembly are wound on an insulating supporting tube 20, which ispreferably of rectangular configuration and may be die formed fromgummed kraft paper. The tube 20 is arranged to receive steel windingmandrel 21, slidable therein (see FIGS. 2 and "3) and having a portionextending from each end of the tube arranged for fastening to a chuckingdevice of a winding machine (not shown). The tube 20 ispreferably-elongated to-provide means for winding a series of axiallyspaced turns thereon. The wires 22 for each of the coil members,designated generally by the reference character C, are fed from supplybobbins 23 and are -'wound toform a layer of a predetermined number ofjuxtaposed convolutions on the coil tube 20. As is disclosed in-FIGS.3-and 5, each of the layers L are flat and particular care is taken toprevent the individual turns from overlapping upon one another in orderto maintain minimum size and to prevent damage during later pressuremolding operations. The wires 22 are received from the manufacturer withan insulating coating and each layer is further insulated from itsadjacent layer by means of casheet 24 of kraft paper. The insulatingsheet 24 is in- "terleaved between the winding layers L and is insertedItherebetween upon completion of a row of juxtaposed coil turns, asshown in FIG. 3. Winding of coil turns :andinsertiomof .the sheets :L iscontinued inthe manner 4 above described until the designated number ofturns have been wound to form the coils C.

In the present case, the assembly disclosed herein, for purposes ofillustration, has particular application for use in electromagneticallyoperated motor starter and contactor devices, although it is Within thescope of the present invention to utilize its teachings for manufactureof electromagnetic coils for use in any electromagnetically actuateddevice requiring a magnetic coil construction, or for that matter, inany device requiring a coil of compact size and wherein coil life is ofimportance.

After winding of the prescribed number of coil turns has been completed,each of the axially spaced coil portions C, wound upon the coil tube 20are separated from one another. This is accomplished upon removal of thetube 20 from the mandrel 21, by simply severing the tube 20 into itsvarious sections at points intermediate the outer turns of each coilportion, such as by means of a band saw blade (not shown). Thus, theindividual coil members take the form of the coil C as shown in FIGS. 4and 5 with extending lea-d portions 25 and 26, to provide a layer woundconstruction of juxtaposed coil wire turns L, separated from one anotherby means of the paper strips 24.

The illustrated coil assembly A may comprise two identical coils C whichare positioned, as shown in FIG. 6, upon a locating and supporting plate27 which may be provided with a centrally located leg portion having aninterruption 28. Since the purpose of the interruption 28 is to preventcirculation of current which would otherwise fiow as the result ofalternating current flux linkage in alternating current coils, it Willbe apparent that this interruption may be made in the outer legs, if sodesired. In the case of interrupting the center leg portion, there is anassumption made that the coils C are substantially identical inelectrical characteristics. Placement of the interruption in the outerlegs would prevent current flow through the plate should the seriesconnected coils not be identical electrical properties. When the coil isto be used with direct current, no interruption is necessary. In thepresent embodiment, the support plate 27 has been further modified toprovide upstanding flanges 29 respectively defining windows 30 in thesupport plate 27. Thus, the upstanding flanges 29 act as a means forlocating and providing additional support for each of coils C byextending inwardly of the bore of the supporting tube 20 of therespective coil. An insulating plate 31 is preferably placed between thecoils C and the support plate 27. The height of these upstanding flangeshas a substantial effect on the shape of the pull curve when'thesupporting plate 27 is made of magnetic material.

After the coils C are mounted in place on the support plate 27, theleads 26 are twisted and soldered together, as shown in FIG. 7, tothereby serially connect the twin coils C. It will be understood thatthe coils C must be connected to aid one another magnetically, but theymay be connected in series or parallel as desired. Next, a terminalassembly, designated generally by the reference numeral 35 (see FIG. 8),is mounted at one end of the coil assembly by means of adhesive contactbetween an insulating paper mounting strip 36 and the outer paper strip24 of the coil C. The mounting strip of paperboard 36, .or the like,serves as. a support for oppositely spaced terminal members 37, eachhaving a tapped opening 38. The terminals 37 are each fastened to themounting strip 36 by means of rivets 39. An insulating paperboard sheet40 is interposed between the head of the rivets 39 and the coil C. Theterminal assembly is fully disclosed in the subassem bly view 0 FIG. 9.

FIG. 9 is also illustrative of the technique of providing a means forprotecting the threads of the'term-inal openings 38 during molding. Thisis accomplished by means of mounting a protective molding insert 45directly over the spaced-apart terminals 37. Screws 46 are each threadedinto respective tapped opening 38 of each of the terminals 37 until theinsert 45 is brought into flush engagement with each of the terminals.As shown in FIG. 10, the respective screws 46 extend inwardly of thetapped openings 38 to further provide a means of preventing the moldingcomposition from interfering with the terminal screws (not shown) whichare later threaded into the terminals 37 as. a means of connecting thecoil with a source of power. The coil assembly, as viewed in FIG. 10, isnow ready for placement in the die cavity of a transfer molding machineor the like. However, a group of assemblies, corresponding in number tothe cavities in the die, are first preheated in an oven (not shown).This serves to drive off volatiles and moisture from the coils, whichmight prevent proper filling of the mold with the heated moldingmaterial or the possible formation of bubbles or blisters.

With reference to FIGS. 11-13, it will be apparent i that the coilassembly, comprising the coils C mounted on the support plate 27, andwith the removable protective insert 45 attached thereto, is arrangedfor placement in the molding cavity 50 of the lower die block 51. Asillustrated in FIG. 11, the coil assembly is disposed with the supportplate 27 resting upon retractable support pins 52 in a manner thatpermits the assembly to be supported in spaced relationship relative tothe bottom surface of the die cavity 50. The detail and operation of thesupport pins 52 are more fully described and claimed in the co-pendingapplication of Roy A. Gill, Ser. No. 178,092, filed on Mar. 7, 1962, nowabandoned, and assigned to the same assignee as the present invention.The technique described therein permits the molding composition 53 tototally encapsulate the assembly during the molding operation ashereinafter described. It will also be apparent that the upper supportpins 54 cooperate with the pins 52 to clamp the coil assembly Atherebetween during the initial molding period until sufficient moldingcomposition has entered the die block cavities to support the assemblyA. The upper block 55 is supported by means of the supporting actuator56 fastened thereto.

The headed upper and lower support pins 52 and 54 are, in turn,respectively supported by the separable b-ar sections 57 and 58 heldtogether in clamping relationship by means of the screws 59. Thus, theheaded support pins. 52 are removably held in place with respect to thebar sections 57 and 58. The same is true of the upper support pins 54,which are clamped to the headed portion of the bar sections 60 and 61fastened together by means of screws 62. Each of the support pin barsare movable relative to one another by means not shown, and for purposeshereinafter set forth. A knockout bar 63 is also provided for supportingknockout pins 64 and is movable upwardly to eject the molded assemblyfrom the die after it has been cured.

The remaining portions of the mold are conventional and comprise acentrally located transfer chamber 76 having a bore adapted to slidablyreceive plunger 71, which is shown in its uppermost position in FIGS. 11and 12 and in its withdrawn position in FIG. 13. In FIGS. 11 and 12, thecoil assembly is shown within the closed upper and lower die blocks 51and 55, respectively, and with the molding material having been injectedinto the cavity 50. The die is gated at 72 :and is provided with runnerswhich form a sprue 73 removable, along with a cull 74 after the dieblocks are separated.

Thus, after the molding composition has been brought to liquefyingtemperature and injected into the die cavities 50, with the coilassemblies A respectively supported therein, the preheated assembliesare uniformly encapsulated with the molding composition 53'. A suitablemolding composition for this purpose is a mineral filled epoxycomposition known as No. 3628 compounded by the Fiberite Corporation ofWinona, Minnesota. When this particular material is used the pressure ismaintained in the neighborhood of 50 to pounds per square inch. Thepressure may be lower or higher depending upon the size and strength ofthe winding wire 22. This pressure range is quite low when compared topressure utilized in conventional molding techniques. The importantconsideration concerning pressure lies in providing suilicient pressurefor flow and coverage of the entire assembly A, including the plate 27,and to compact the windings into a solid unit and, at the same time,avoid damaging the coil windings, terminals or connections therebetween.

The particular molding composition, above-described, contains nosolvents or other material that might damage the original insulatingcoating deposited on the coil wire. However, the curing temperaturewould have an adverse effect if it were maintained for any length oftime. It is desirable to use :a composition, such as that mentionedabove, which cures in a short time. It will be apparent that theselection of such molding materials is an important aspect of thepresent invention. In addition, no solvents or carriers are used whichmight volatilize during the heated molding operation and thereby leavevoids which would interfere with the heat conducting characteristics ofthe pressure molded mass and compacted coil. Since there is noimpregnating compound within the windings to swell when overheated, theability of the finished molded coil to resist undesirable swelling andblistering when overheated is determined largely by the characteristicsof the molding compound. The above-mentioned Fiberite Corporationcomposition No. 3628 is suitable in this respect.

The total mold and cure cycle for the above-mentioned composition isapproximately 4 minutes, although it will be obvious to those skilled inthe art that such period may vary with composition, preheat temperature,etc. In the present case, the composition has a usable flow period ofapproximately 60 seconds and the pressure is applied to the ram plunger71 for a period of approximately 2.5 minutes. The retractable supportpins 52 and 54 are 'maintained in clamping position relative to theassembly A for a period of from 12 to 35 seconds (depending upon ambienttemperature, humidity, composition, etc.) to permita desired amount ofthe composition to flow into the cavities Stl. The support pins 52 and54 are then retracted to the position shown in FIG. 12. This will permitthe material to fill the entire cavity, and thereby provide a uniform,non-Interrupted encapsulating coating surface.

No areas will remain which would otherwise require patching, filling orother attention.

As stated previously, the construction and operation of the retractablepins 52 and 54 are more fully described and claimed in theaforementioned co-pending application of Roy A. Gill, Ser. No. 178,092.Upon completion of the 4 minute cycle, the die block 51 and 55 areseparated. Removal of the assemblies A from their respective cavities isdelayed for a period of 18 to 30 seconds, depending upon atmosphericconditions, to permit the encapsulating surface to cool and furtherharden. The knockout pins 64 are then moved to the position shown in theview of FIG. 13 by means of the knockout bar 63 to raise the hardenedencapsulated coil assembly A upwardly from the cavity 50, along with theinsert 45 for removal thereof. The cull 74 and sprue 73 are also removedwith the finished pieces, and are broken away from the pieces by hand.The ram or plunger 71 is then retracted for receipt of :a new preheatedmolding composition preform. The knockout pins 64 are also retracted tothe position shown in FIGS. 11 and 12, and the coil support pins 52 and54 are extended outwardly from the blocks 51 and 55, respectively, tothe position shown in FIG. 11 for support of a new coil.

The interior surface of the coil molding insert 45 is preferablyroughened to provide the complementary roughened surface 80 at the oneend of the assembly A, as shown in FIG. 14 which more readily receives aprinted identification or label. Inasmuch as the molding composition isof an epoxy type, it will be appreciated that the surfaces must beroughened or otherwise treated for receiving printing inks or adhesive.Thus the inherent roughness provided in this area during molding is ofadvantage.

It will be apparent from the enlarged cross section of FIG. 18 that thepressure molded assembly of the present invention provides anarrangement of coil windings in layer-Wound relationship and which arecompressed into a compact, tightly held body by means of anencapsulating molding composition, and wherein the said moldingcomposition contacts only the coil ends so as not to affect theinsulation normally coating the coil wire. From FIG. 18, it will benoted that the coil turns in the layers L are compressed towards oneanother in side-by-side contact. In coils wound with fine wire andinsulated with relatively thin insulating paper layers 24,.there is atendency of the paper layers 24 to fold over the ends of the windinglayers L to cover these windings, depending upon mold gating, andthereby help in preventing the composition to be in direct contact withthe windings on the insulation thereon. There does not appear to be anyappreciable effect upon the wire insulation though when the paper layers24 are relatively thick and the wires are of relatively large diameter.

It will be further apparent that by utilizing the herein disclosedpressure molding technique, that the molding pressure acts to uniformlycompact the conducting turns of the coil or coils into a relativelysolid mass with adjacent turns in physical contact. It is well known bythose familiar with the axioms of heat transmission that heat -will bedissipated from a solid mass more readily than in instances whereinthere may be occluded gas pockets between adjacent winding turns, aswould be the case with conventional varnish impregnated coils (with orwithout vacuum). These materials generally contain volatile solvents,which when later evaporated leave gas filled voids acting as localizedheat insulators.

In addition to the advantages of increased heat conduction accomplishedby the techniques of the present invention, it will be furtherappreciated that the compact,'pressure molded coil assembly alsoprovides a substantially vibration-free construction wherein theadjacent turns will be prevented from rubbing against one another andwearing off the protective insulating coating and thereby shorting outcertain sections of the coil. There is no impregnating varnish or resinin the interstices of the winding which might otherwise cause swellingor blistering if the coil should he accidentally overheated.

The coil assembly of the present invention is dimensionally;stable andlends itself to cleanfstraightforward production techniques ashereinabove described.

Although the present assembly has been described with reference to aparticular embodiment thereof, it is, of course, to be understood thatthis invention is not to be so limited, except as so defined by theappended claims.

I claim:

1. A pressure molded electrical coil comprising a plu- -rality of layersof convoluted turns of an insulated conductor and defining alongitudinal opening therethrough, the conductor turns of a respectivelayer lying in substantial side-by-side relationship, said layer-s beingseparated from one another by means of interleaving insulating sheetmaterial, a supporting and locating plate disposed adjacent one side ofsaid coil and being formed to provide a window defined by upstandingmarginal portions protruding partially into the longitudinal opening ofsaid coil, an insulating plate disposed between said supporting plateand said coil, a thermoset encapsulating compound surrounding said coilturns and said supporting plate to compact said turns and said sheets asa solid unit; said unit and said encapsulating material defining intheir adjacent relationship a substantially distinct marginal line ofdemarcation.

.2. A pressure molded electrical coil comprising two adjacent coilwindings each having a plurality of layers of convoluted turns of aninsulated conductor and each defining a longitudinal openingtherethrough, the conductor turns of a respective layer lying insubstantial sideby-side relationship, said layers being separated fromone another by means of interleaving insulating sheet material, asupporting plate disposed adjacent one side of said coil windings andbeing formed to provide two coil winding windows, each defined byupstanding marginal locating portions protruding partially into thelongitudinal opening of a respective coil winding, said plate furtherincluding an interrupted leg portion adjacent a window therein, wherebyan electric current path will be interrupted in said plate where thereis a voltage induced therein, an insulating plate disposed between saidsupporting plate and said coil windings, a thermoset encapsulatingmaterial surrounding said coil windings and said supporting plate tocompact said turns and said sheets as a solid unit; said unit and saidencapsulating material defining in their adjacent relationship asubstantially distinct marginal line of demarcation.

3. A pressure molded electrical coil comprising two adjacent coilwindings each having a plurality of layers of convoluted turns of aninsulated conductor and each defining a longitudinal openingtherethrough, the conductor turns of a respective layer lying insubstantial side-by side relationship, a supporting plate disposedadjacent one side of said coil windings and being formed to provide tw-ocoil winding windows, each defined by upstanding marginal locatingportions protruding partially into the longitudinal opening of arespective coil winding, said plate further including an interrupted legportion adjacent a window therein, whereby an electric current path willbe interrupted in said plate where there is a voltage induced therein,an insulating plate disposed between said supporting plate and said coilwindings, athermoset encapsulating material surrounding said coilwindings and said supporting plate to compact said turns as a solidunit; said unit and said encapsulating material defining in theiradjacent relationship a substantially distinct marginal line ofdemarcation.

References Cited by the Examiner UNITED STATES PATENTS 1,864,331 6/ 1932Whitesmith 336-205 1,884,385 10/1932 Thordarson 336-197 X 2,411,81011/1946 Sander 3 36-178 X 2,464,029 3/ 1949 Ehrman 336-96 X 2,478,633 8/1949 Lord 336-205 2,490,506 12/1949 Brouerman 336- X 2,724,869 11/ 1955Merrill 1 8-59 X 2,754,569 7/1956 Kornei 29-15557 2,775,742 12/1956Bogue 336-96 X 2,856,639 10/1958 Forrest 18-59 2,930,011 3/1960 Wigertet a1. 336-96 2,942,217 6/1960 Ford 336-205 2,960,755 11/1960 Bender etal. 29-15557 3,030,597 4/ 1962 Piaia et a1. 264-272 X ROBERT K.SCHAEFER, Primary Examiner.

JOHN F. BURNS, LARAMIE E. ASKIN, Examiners.

T. I. KOZMA, Assistant Examiner.

1. A PRESSURE MOLDED ELECTRICAL COIL COMPRISING A PLURALITY OF LAYERS OFCONVOLUTED TURNS OF AN INSULATED CONDUCTOR AND DEFINING A LONGITUDINALOPENING THERETHROUGH THE CONDUCTOR TURNS OF A RESPECTIVE LAYER LYING INSUBSTANTIAL SIDE-BY-SIDE RELATIONSHIP, SAID LAYERS BEING SEPARATED FROMONE ANOTHER BY MEANS OF INTERLEAVING INSULATING SHEET MATERIAL, ASUPPORTING AND LOCATING PLATE DISPOSED ADJACENT ONE SIDE OF SAID COILAND BEING FORMED TO PROVIDE A WINDOW DEFINED BY UPSTANDING MARGINALPORTIONS PROTRUDING PARTIALLY INTO THE LONGITUDINAL OPENING OF SAIDCOIL, AN INSULATING PLATE DISPOSED BETWEEN SAID SUPPORTING PLATE ANDSAID COIL, A THERMOSET ENCAPSULATING COMPOUND SURROUNDING SAID COILTURNS AND SAID SUPPORTING PLATE TO COMPACT SAID TURNS AND SAID SHEETS ASA SOLID UNIT; SAID UNIT AND SAID ENCAPSULATING MATERIAL DEFINING INTHEIR ADJACENT RELATIONSHIP A SUBSTANTIALLY DISTINCT MARGINAL LINE OFDEMARCATION.